docs: add some more docstrings to DMM, nicked from the Confluence page

src/fixate/drivers/dmm/__init__.py

@@ -1,11 +1,13 @@
 """
 dmm is the digital multimeter driver.
 
-Use dmm.open to connect to a connected digital multi meter
-Functions are dictacted by the metaclass in helper.py
+Use dmm.open to connect to a connected digital multimeter.
+Functions are dictated by the abstract superclass ``DMM`` in helper.py
 
-dmm.measure(*mode, **mode_params)
-dmm.reset()
+::
+
+    dmm.measure(*mode, **mode_params)
+    dmm.reset()
 """
 import pyvisa
 
@@ -18,6 +20,9 @@
 
 
 def open() -> DMM:
+    """
+    Connect to a digital multimeter.
+    """
     for DMM in (Fluke8846A, Keithley6500):
         instrument = find_instrument_by_id(DMM.REGEX_ID)
         if instrument is not None:

src/fixate/drivers/dmm/helper.py

@@ -38,24 +38,44 @@ def measurement(self, delay=None):
         raise NotImplementedError
 
     def voltage_ac(self, _range=None):
+        """
+        Sets the DMM in AC voltage measurement mode and puts it in the range given
+        by the argument _range. Signals expected to be measured must be < _range.
+        """
         raise NotImplementedError
 
     def voltage_dc(self, _range=None, auto_impedance=False):
+        """
+        Sets the DMM in DC voltage measurement mode and puts it in the range given
+        by the argument _range. Signals expected to be measured must be < _range.
+        """
         raise NotImplementedError
 
     def current_ac(self, _range):
         raise NotImplementedError
 
     def current_dc(self, _range):
+        """
+        Sets the DMM in DC current measurement mode and puts it in the range given
+        by the argument _range. Signals expected to be measured must be < _range.
+        """
         raise NotImplementedError
 
     def resistance(self, _range=None):
+        """
+        Sets the DMM in 2-wire resistance measurement mode and puts it in the range 
+        given by the argument _range. Signals expected to be measured must be < _range.
+        """
         raise NotImplementedError
 
     def frequency(self, _range=None):
         raise NotImplementedError
 
     def fresistance(self, _range=None):
+        """
+        Sets the DMM in 4-wire resistance measurement mode and puts it in the range 
+        given by the argument _range. Signals expected to be measured must be < _range.
+        """
         raise NotImplementedError
 
     def period(self, _range=None):